To analyze the morphogenesis and structure of the virus-like particles associated with the L2C transplantable leukemia of the guinea pig and to compare these virus particles to the type B virus induced in tissue cultures of guinea pig cells by 5-bromo-2' deoxyuridine. This comparison was both morphological and biochemical. To examine the histopathological host response resulting from a variety of therapeutic protocols as applied to tumor systems of the mouse, rat and guinea pig.